This project focuses upon the role of hydrostatic pressure gradients in the formation and resolution of ischemic brain edema. We intend to use middle cerebral artery occlusion in cats to establish focal ischemia and edema. We expect to find that pressure gradients develop within ischemic tissue and that they may be detected using the tissue pressure method we have modified. By coupling tissue pressure measurements with those of brain water, rCBF, blood-brain-barrier integrity, and osmolality of tissue and serum, we expect to clarify the relationships of cellular swelling, fluid extravasation, and bulk flow of fluid in the ischemic edema process.